Globoid cell leukodystrophy is a rare autosomal recessive genetic disease caused by low levels of B-galactosidase activity, a lysosomal enzyme important in myelin metabolism. An infant rhesus monkey with this disease was diagnosed at TRPRC in 1989. In the intervening nine years, we intentionally inbred this group of animals and in 1996 observed two additional affected infants. These two homozygous affected animals allowed us, in collaboration with Dr. David Wenger, Jefferson Medical College, Philadelphia, to identify the disease-causing mutation in the rhesus GALC gene and to unequivocally identify 22 carrier animals by PCR. The sequence of the rhesus GALC cDNA is 98% identical to the human, and the deduced amino acid sequence is 97% identical to that of humans. The mutation responsible for GLD in these monkeys consists of the deletion of the AC dinucleotide corresponding to cDNA positions 387 and 388. This results in a frame shift, leading to a premature stop codon. GALC activity was measured in the 2 homozygous affected, 21 normal and 20 carrier monkeys. The 2 affected infants had a GALC activity less than 2% of normal. The average activity for 21 normal monkeys was 0.94 nmol/hr/mg of protein, while the average for 20 carriers was 0.53. Psychosine levels in the brains of affected infants were very high. These results have been published (Luzi P, Rafi MA, Victoria T, Baskin GB, Wenger DA. Characterization of the rhesus monkey galactocerebrosidase (GALC) cDNA and gene, and identification of the mutation causing globoid cell leukodystrophy (Krabbe disease) in this primate. Genomics 42:319-324, 1997; Baskin GB, Ratterree M, Davison BB, Falkenstein KP, Clarke MR, England JD, Vanier MT, Luzi P, Rafi MA, Wenger DA. Genetic Galactocerebrosidase deficiency (globoid cell leukodystrophy, Krabbe disease) in rhesus monkeys. (SUBMITTED). We established fibroblast and EBV-transformed lymphocyte cultures from these homozygous infants, and have initiated in vitro therapeutic studies with retroviral vectors containing the human GALC gene. This nonhuman primate model will be valuable for studies of gene therapy of this and similar disorders. A grant application to support this